An order blocking filter (OBF) must be used to prevent spectral overlapping of the of the first and second order diffraction, thereby extending the usable wavelength range of the transmission diffraction grating spectrograph. The different wavelengths are diffracted to angle β according to the grating equation:
m λ = d (sin α + sin β)
Where m is the diffraction order (0, ±1, ±2…), λ is the wavelength, d is the groove spacing, and α is the incoming angle. Since there is more than one wavelength that satisfies this equation for a particular set of values, there can be overlapping orders of spectra falling on the same space on the detector.
The OBF has a long pass filter coating on 50% of the surface to block wavelengths below a specific wavelength. Several different order blocking filters (OBFs) are available for use with ImSpector imaging spectrographs, and an OBF must be used with the ImSpector UV4E, V10, V10E, and N25E. Hyperspectral cameras include the OBFs as required by the camera. However, an OBF must be ordered separately when ordering a spectrograph independent of a hyperspectral camera.
The OBF can be installed either as a plain filter or with a C-mount holder. The OBF must be positioned between the spectrograph and
the detector, as close as possible to the detector, and oriented with the coated half of the filter on the longer wavelength side of the
|OBF Model||Size||Mechanical C-mount Holder Available||Suitable ImSpector Model|
|OBF UV4E||Rectangular, 14 mm x 12 mm||No||UV4E|
|OBF 450||Circular, Ø 17 mm||Yes (lockable)||V8(E)|
|OBF 570||Circular, Ø 17 mm||Yes (lockable)||V10(E)|
|OBF 570||Circular, Ø 20 mm||Yes (lockable)||V10(E)|
|OBF 570||Rectangular, 14 mm x 12 mm||Yes (lockable)||V10(E)|
|OBF 1400||Rectangular, 18 mm x 18 mm||No||N25E|
|Order Blocking Filter Ordering Information|
|Part number||Description||Product Name|
|MRC-310-001-01||Visible Range Order blocking filter, V8/V8E, Ø 17 mm||OBF45017|
|MRC-310-001-02||Visible Range Order blocking filter, V8/V8E, Ø 17 mm, C-mount||OBF45017C|
|MRC-310-002-01||VNIR Range Order blocking filter, V10/V10E, 14 x 12 mm||OBF57014|
|MRC-310-002-02||VNIR Range Order blocking filter, V10/V10E, 14 x 12 mm, C-mount||OBF57014C|
|MRC-310-002-03||VNIR Range Order blocking filter, V10/V10E, Ø 17 mm||OBF57017|
|MRC-310-002-04||VNIR Range Order blocking filter, V10/V10E, Ø 17 mm, C-mount||OBF57017C|
|MRC-310-002-05||VNIR Range Order blocking filter, V10/V10E, Ø 20 mm||OBF57020|
|MRC-310-002-06||VNIR Range Order blocking filter, V10/V10E, Ø 20 mm||OBF57020C|
|MRC-310-004-01||UV Range Order blocking filter for UV4E, 14 mm x 12 mm||OBFUV4E|
|MRC-310-005-01||SWIR Range Order blocking filter for N25E, 18 mm x 18 mm||OBF1400|
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